WEDNESDAY, July 1, 2015 (HealthDay News) -- The injectable drug Saxenda may be a helpful tool in the battle against excess weight and obesity, a new study suggests.

People who injected Saxenda (liraglutide) every day for a year lost an average of 18.5 pounds, compared with an average of 6 pounds for those taking a placebo, researchers found.

Saxenda "can lower weight, improve cardiovascular risk factors and improve quality of life," said lead researcher Dr. F. Xavier Pi-Sunyer, professor of medicine at Columbia University Medical Center in New York City.

"It can also reduce the progression to type 2 diabetes from prediabetes," he said.

In a lower-dose version called Victoza, liraglutide is approved for diabetes treatment.

For the study, funded by the maker of Saxenda, Novo Nordisk, researchers recruited more than 3,700 overweight or obese people without diabetes . Participants were assigned to daily injections of Saxenda or placebo for 56 weeks. Both groups also received lifestyle counseling. More than half had prediabetes.

Sixty-three percent of patients taking Saxenda lost at least 5 percent of their initial body weight, and one-third lost more than 10 percent of body weight, the researchers found. Among those receiving placebo, 27 percent lost 5 percent of their body weight, and one in 10 lost more than 10 percent of their body weight.

Losing 5 percent of body weight -- 14 pounds for someone at 280 -- can have a significant positive effect on the risk for diabetes and heart disease, Pi-Sunyer said.

In the United States, more than two-thirds of adults are overweight or obese, according to a recent study in JAMA Internal Medicine.

"This medication adds to the options physicians will have in helping overweight and obese patients lose weight and keep it off," Pi-Sunyer said.

The study was published July 2 in the New England Journal of Medicine.

Other drugs approved for weight loss in the United States include Orlistat (Xenical), lorcaserin (Belviq), phentermine-topiramate (Qsymia) and naltrexone-bupropion (Contrave). But many users complain of side effects.

The most common side effects with Saxenda were mild or moderate nausea and diarrhea. Serious side effects occurred in 6.2 percent of patients taking Saxenda and in 5 percent of those receiving the placebo, the researchers report.

However, the drug is expensive, said Dr. Joel Zonszein, director of the clinical diabetes center at Montefiore Medical Center in New York City.

Although covered by most of the insurance plans and Medicare, "it has a high co-pay of $20 to $100, as it is not generic," Zonszein said. "The price in the U.S. is between $1,000 and $1,800 for a three-month supply."

Dr. Elias Siraj, director of the diabetes program at Temple University School of Medicine and Hospital in Philadelphia, said it's important to remember that obesity is a lifestyle condition.

"We should not lose sight of the need to adjust lifestyle -- diet and exercise," he said. "Medications, too, can be helpful."

The unanswered question about Saxenda is whether people can maintain their weight loss over time, especially when the medication is discontinued, said Siraj, co-author of an editorial accompanying the study.

Because the drug is injectable and costly, Siraj doesn't think it's for everybody. "But for some patients I think it is going to be a significant tool, but we have to wait for longer studies," he said.

"We are dealing with an obesity epidemic and it hasn't been easy to tackle obesity," he said. "We need a lot of tools. This medication, hopefully, will be one of the tools."